Ascorbic acid and oxidative inactivation of proteins

A number of active oxygen species are likely implicated in the etiology or manifestation of several pathological conditions, including aging, arthritis, carcinogenesis, atherosclerosis, and muscular dystrophy. Ascorbate plays a key role in protecting cells against oxidative damage. Paradoxically, in the presence of Fe3+or Cu2+, ascorbate can promote the generation of the same reactive oxygen species ( · OH, O2−, H2O2, and ferryl ion) it is known to destroy. This prooxidant activity derives from the ability of ascorbate to reduce Fe3+or Cu2+to Fe2+or Cu+, respectively, and to reduce O2to O2− and H2O2. Damage to nucleic acid and proteins results from the binding of either Fe2+or Cu+to metal binding sites on these macromolecules followed by reaction of the metal complexes with H2O2; this leads to the production of active oxygen species that attack functional groups at or near the metal binding sites.